Peat

Peat, living and partially decomposed organic matter, consists principally of decayed brown mosses, Sphagnum plants, sedges and other semiaquatic plant remains. Peat is formed slowly in water-logged areas by the decay of vegetation, mostly under anaerobic (oxygen-deficient) conditions, and contains up to 95% water by weight. Canada's extensive peatlands developed since the last glaciation, about 10 000 years ago. The high water content has always been the main obstacle to its extensive exploitation as an energy source; however, dried peat has been one of the traditional fuels in places where the peat is of high quality and easily accessible (eg, Ireland). Other uses of peat include water filtration, absorbent materials and horticultural applications, including the cultivation of vegetables on peatlands in southern Québec.

Importance

Peat is important because it stores organic carbon that otherwise could be released into the atmosphere as carbon dioxide or methane, "greenhouse" gases that affect global climate. Canadian scientists are studying peat to learn more about past and present climate trends (see Climate change). Peatlands are also ecosystems of plants and animals that thrive under harsh conditions: they are sometimes called "nature's nurseries." In addition, there is considerable interest in the potential industrial uses for peat.

Peatlands are fens, swamps, marshes and bogs that cover approximately 12% of Canada's land surface, or more than 100 million ha. They can occur in rainy climates such as those on the East and West coasts or in areas with poor drainage and high water tables. Most Canadian peatlands are located in inaccessible northern areas, including what is considered the world's largest contiguous peatland, covering an area of 300 000 km², in the Hudson Bay Lowlands. However, significant deposits occur in the Atlantic provinces, southern Québec, Ontario and Manitoba. Peat has a carbon content of greater than 17% by weight.

Use

Canadian peat resources, estimated at 335.4 billion t dry weight, are among the largest in the world. The peat could be used for energy production, particularly in remote areas and where other resources are lacking; however, at present Canadian peat is recovered exclusively for other industrial and horticultural purposes. These include use as a soil supplement in horticulture, as a filter for domestic and industrial waste water, as an absorbent in sanitary products and animal litter, and in decorative products such as flower jars. Peat has also been used to help clean up oil spills (see Water pollution). The microscopic pores of Sphagnum plants make these mosses 3-4 times as absorbent as cotton wool, while their natural acidity gives them antiseptic properties.

Interest in peat fuel increased in Canada during the 1970s and 1980s, and it was shown to be an economical alternative to oil or coal-fired electric-power generating stations in some circumstances. A number of full-scale tests showed that peat is a feasible alternative fuel either in solid or in gasified form. Another option would be to produce methanol from peat-derived synthetic gas.

Locations

In Europe, extensive research and development programs exist, and the technology of harvesting and use of peat is well developed. More than 6000 MW of Russia's electric power, equivalent to over 6% of Canada's electrical generation, is peat-fired, and, in addition, about 4.5 million t of peat are produced annually for home heating. Finland and Sweden have several peat-burning power stations that produce electricity and provide steam and hot water for district heating. Peat-fired power stations, if located more than 60 km from ports of imported oil sources, are cost-effective power alternatives. Ireland obtains about one-third of its electric power from 7 peat-fired generating stations, which consume about 56% of Ireland's annual peat harvest of 5 million t. In Canada, the National Research Council of Canada has established a Peat Program designed to define Canada's peat resources, to develop harvesting and utilization technology, to assess and reduce environmental impacts and to develop carbon-added products.

Because peat contains up to 95% water, it cannot support heavy machinery; removal of as much moisture as possible is essential for the preparation of a bog for harvesting. In a typical method, a network of drainage ditches begins the process; the ditches are deepened as the peat consolidates. This takes normally 5-7 years and reduces the bog's water content to about 90%. After drainage, the bog is levelled to facilitate drying and mechanical handling. In some large bogs a network of narrow-gauge railways are built on the bog's surface for the removal of the peat to the packaging plant. The bog is then ready for decades of harvesting, typically at a rate of a few centimetres per year, as the surface dries.

Natural Peatlands Are Living Ecosystems

Natural peatlands are living ecosystems where distinct plant and animal communities live. Peatlands are the home of a variety of unique insect-eating plants as well as a host of orchid species. Peatlands are an important part of wildlife habitats, such as woodland caribou, moose and others. There are a large variety of peatlands, formed mainly in response to water quality. Bogs derive their water and nutrient source from rainwater. Their surface is a continuous carpet of Sphagnum mosses that can thrive in the acid, water-logged environment. Low shrubs and stunted trees may also be present. In contrast, fens are nourished by a moving water table that is enriched by mineral nutrients. Such fens are dominated by sedges and brown mosses, as well as tall shrubs or trees.

The peat of bogs and fens may differ in their floristic compositions, but they are all support a living surface layer, underlain by a fibrous recent peat that, in turn, rests on more decomposed peat, which typically becomes darker and denser with depth until the black colour and puttylike consistency of old peat is encountered. However, the decomposition does not always increase from top to bottom; in bogs, less decomposed fibrous material may often be found under more decomposed material.

Harvesting

When peat is harvested for use, the surface living layer is destroyed to expose the desired peat. The harvesting removes the peat that has taken thousands of years to develop, accumulating at an average rate of 5 cm per century. After the peat extraction is completed, perhaps decades later, the abandoned field becomes flooded with water. The wetland formation process will be set back thousands of years. Rehabilitation of the mined-out peatland can promote the establishment of a productive wetland. Scientists from Laval University and the University of Alberta have been working on a project to restore harvested peatlands back to a similar peat-accumulating environment. Despite some success, much work remains to be done.

See also muskeg.